The present invention relates to cabling methods and apparatus, and more particularly to a method of and an apparatus for making twisted cable products, such as, for example, 600 volt secondary underground distribution (UD) cable, in a continuous in-line process.
There are several well known methods of and apparatus making twisted electrical cable products. For example, U.S. Pat. Nos. 3,686,843; 4,133,167; 4,171,609; 4,215,529; 4,426,837; 5,239,813; and 5,557,914 disclose a few of the many different types of twisting and cabling methods and apparatus which are used for twisting conductors or wires and for making twisted electrical cables. In another conventional method, a plurality of aluminum or copper wires is stranded together into a single bare stranded conductor which is then insulated with a polymeric insulation, preferably by extrusion. The extruded insulation is cured and the insulated stranded conductor is wound onto a reel, tested on its reel which is then stored for later use. Two or more of the reels of insulated stranded conductor are taken from storage and mounted in a cabling apparatus for simultaneous pay out. As the conductors are payed out from the reels, they are twisted together to form a twisted cable and the twisted cable is taken up on a reel. Typically, each insulated conductor is payed off its reel in an untwisted condition, and the conductors are then twisted together in a planetary assembly, i.e., without each individual conductor being twisted about its own longitudinal axis, by rotation of the cable takeup reel.
The aforementioned conventional method has been used heretofore to manufacture secondary electrical distribution cable, such as, for example, 600 volt triplex UD cable, and represents the state-of-the-art for manufacture of such cable. One disadvantage of the conventional method is large number of manufacturing steps involved in the manufacture of the cable. The number of manufacturing steps is increased in part because of the requirement to provide in-process handling and inventory control of the large reels of uninsulated bare conductors, of copper or aluminum, as well as in-process handling and inventory control for the same large reels after the insulation material has been extruded onto the uninsulated bare conductors and cured to form the insulated conductors that are subsequently cabled together into the twisted electrical distribution cable. Substantial in-process storage space is also required for both the large reels of bare stranded conductors, as well as for the equally large reels of insulated stranded conductors. In addition, each extrusion line for applying the plastic insulation to the conductors requires substantial plant floor space for the equipment necessary to unreel the bare stranded conductor, extrude the insulation onto the stranded conductor, cure the insulation and take-up the insulated stranded conductor on a reel. Substantial floor space is especially required for the cooling troughs necessary to cure the insulation material before the insulated stranded conductor is taken up onto a reel.
It would be desirable, therefore, to provide a method and an apparatus that reduces the in-process handling steps, the in-process storage and plant floor space requirements necessary for the conventional method and apparatus for making twisted electrical cable, such as 600 volt secondary distribution cable.
In view of the foregoing limitations and shortcomings of the prior art methods and apparatus, as well as other disadvantages not specifically mentioned above, there is still a need in the art to improve the processing of and the apparatus for manufacturing twisted electrical cable. The present invention is directed to an improved method of and an apparatus for making twisted cable and the cable manufactured thereby. The method and apparatus of the invention overcome most, if not all, the disadvantages of the prior art methods and apparatus as more fully described hereinafter.
According to the broadest aspects of the method and apparatus of the present invention, a plurality of reels containing bare stranded conductors, e.g., 19 wire stranded aluminum conductors, are mounted for simultaneous pay out of the bare stranded conductors from a plurality of stationary pay out stations. Means are provided for the simultaneous changeover or replacement of spent pay out reels with a new set of full reels of stranded conductors, including a welding station for each pay out station for welding the trailing end of a payed out stranded conductor to the leading end of a stranded conductor to be payed out. The bare stranded conductors are fed from the pay out stations to a plurality of pay out accumulators, one for each pay out station, where the conductors are accumulated during the simultaneous changeover of the stationary pay out reels and welding of the stranded conductor ends between reels.
Each of the plurality of bare stranded conductors is fed from a respective pay out accumulator separately to an extrusion station where a plastic insulation material such as silane XLPE, is extruded onto each stranded conductor. For instance, in the case of the manufacture of a 600 volt triplex secondary distribution cable, the extrusion station may include either three separate extruders each feeding a respective extrusion crosshead and extrusion die or single or multiple extruders feeding single or multiple extrusion crossheads with multiple (advantageously three) separate extrusion dies. Preferably, a conventional stripe extruder is provided at the extrusion station for extruding surface striping, e.g., three stripes 120xc2x0 apart, on one of the three extruded plastic insulations to identify the neutral conductor. The locations of the welds in each stranded conductor are marked downstream of the extruders for a purpose to be described.
After the plastic insulation is extruded onto each stranded conductor, the plastic insulation is cooled and may be cured if required, by passing the insulated conductors simultaneously through a common water cooling trough downstream of the extruder station. After cooling and/or curing of the plastic insulation, the individual insulated conductors are fed downstream to a respective take up accumulator used to accumulate the insulated stranded conductors during changeover of the twisted cable take-up reel. From the take-up accumulators, the insulated stranded conductors are guided through a closing die and thence to a rotating take-up capstan and a take-up reel or a rotating reel take-up apparatus. The rotating reel take-up apparatus or rotation of the take-up capstan twists each individual insulated conductor about its longitudinal axis and the plurality of insulated conductors are twisted about each other as the take-up reel simultaneously takes up the twisted cable. When the marked welds in the individual insulated stranded conductors of the twisted cable approach the take-up reel, reeling is stopped and the insulated stranded conductors are accumulated on the take-up accumulators. The welds are then cut from the twisted cable and at the same time the full take-up reel is removed and replaced by an empty take up reel.
Because the finished twisted cable cannot have any welds in the conductors, the welds are cut out of the conductors of the finished twisted cable before the cable is reeled onto the take-up reel. Accordingly, the welds between the trailing ends of the conductors on spent pay out reels and the leading ends of the conductors on replacement pay out reels must pass through the cabling apparatus at substantially the same time, ie., at the same longitudinal positions relative to one another. If the welds in each insulated conductor are longitudinally spaced from one another a substantial distance during manufacture of the twisted cable, a large section of the twisted cable must be cut out and scrapped to insure that no welds remain in the finished twisted cable. For that reason, the welding operations for connecting the conductors payed out from the stationary pay out reels are preferably simultaneously performed on all conductors at the same upstream location to avoid unnecessary scrap of the finished twisted cable.
With the foregoing and other advantages and features of the invention that will become hereinafter apparent, the nature of the invention may be more clearly understood by reference to the following detailed description of the invention, the appended claims and the several views illustrated in the drawings.